The 99 - up Mustang GT and Cobra shifter knobs are very close in size to the SC knobs, but are also slightly different colour too ... dark grey as opposed to black. Same stupid M12 x 1.75 thread size. I sold one to Les Borda for his Cougar, looks good in there, and the price was right at $36 CAN vs. about $120 CAN for the original SC knob. The Ford number is XR3Z 7213 BA, I'm guessing about $25 to $30 should get you one in the U.S. The 94 - 98 Cobra knobs are black, but they are much smaller in size.
cheers
Ed Nicholson
SCCoO